Nine-year-old Oskar has 'heavy boots', his own idiosyncratic term for sadness. Two years ago, his father, Thomas, died in the attack on the World Trade Centre and Oskar remains haunted by five answering-machine messages that Thomas left in the hours before his death.

The precocious Oskar could not be from anywhere except New York. A prepubescent Woody Allen type, he 'doesn't eat anything with parents' and compulsively invents devices to ease human pain. When he finds a key in his father's wardrobe marked with the name Black, Oskar finds the quest he needs, a bleak corollary to the treasure hunts that Thomas used to set. There are 472 Blacks in the city and Oskar resolves to find them all.

Interspersed with his bizarre and often poignant encounters with the city's Blacks are two long letters from his grandparents, estranged since Thomas's conception. They conspire in fragmentary narratives. His grandfather describes the bombing of Dresden, which the couple barely, survived; his grandmother recounts 9/11, which their son did not.

Absence exerts a terrible weight on the living and Thomas is literally absent: his coffin empty, his body never recovered. Oskar, too, 'longs to be empty', while his grandparents, in an effort to contain the losses they have suffered, create 'Nothing Places' in their apartment where they may join the ranks of the disappeared. But as the three stories dovetail, the family discovers remarkable ways of filling the empty space.

In capturing these strange tales of love and grief, Foer pushes language to implosion point. At times, the text gives way under the pressure. Pages of photographs, drawings and numbers are co-opted to communicate what ordinary language can no longer reach.

For all the pyrotechnics, Foer is at his most powerful when he tells the story straight. The Dresden sequence is an astonishing evocation of the horrors of war. Although the book concludes with a much-wished-for fantasy, it is his ability to bear witness to reality that is Foer's greatest strength.